The present invention relates generally to lead assemblies for use with cardiac pacer apparatus, and more particularly to improved sealing systems for lead connectors in cardiac pacer necks.
In the ordinary use of cardiac pacers, it is desirable to place the cardiac pacer circuitry and batteries in an apparatus located in the body but remote from the heart to have more room and to facilitate replacement of the pacer upon depletion of its batteries. A flexible lead is usually provided to connect this pacer apparatus to the desired stimulation site in the heart. Adequately attaching one end of this flexible lead to heart muscle tissue is one concern of the art. Another, with which this invention is concerned, is the safe and secure attachment of the other end of the lead to the pacer apparatus.
This connection is ordinarily accomplished by the insertion of an exposed terminal pin of the lead into an electrical terminal in the neck of the pacer apparatus, the electrical terminal being set inside a cylindrical bore through the pacer neck. The lead is disposed normally in a tubular connector which must sealingly engage the inside wall of the cylindrical bore to maintain free of body fluids the connection between the lead terminal pin and the pacer terminal. Leakage of body fluids beyond the bore into the terminal connection would adversely affect the connection; an adequate and durable seal against such leakage must be maintained.
One approach of the prior art is to provide a pair of compressible rings, axially spaced apart, on the tubular connector coaxially supporting the terminal pin. Such a system is shown, for example, in U.S. Pat. No. 4,072,154. Since the sealing rings must have some extra compressibility to allow ease in the insertion of the lead into the pacer apparatus, however, body movement may cause pivotal movement of the tubular connector in the pacer neck.
If the outermost ring in such a system loses sealing contact with the pacer neck bore because of such movement, body fluids may seep past it. In such cases, the innermost seal generally does not break contact with the inner wall of the bore since the turning moment acting upon it is small and the normal compressibility of the elastomer of which the connector is made maintains a sealed interface. However, if body fluids do leak past the outermost seal, when that seal returns to its predeflected state it may act as a pump and compress the trapped fluid, forcing it forward past the inner seal.
Accordingly, it is an object of the invention to provide a pacer lead sealing system that reduces the possibility of body fluid leaking past, and allows greater pivotal movement of the connector without breakdown of the seal.
Other objects of the invention are to allow for wider manufacturing tolerances for the seals without reducing or jeopardizing their effectiveness, to allow greater seal pressures to be achieved without increasing the force necessary to insert the connector, to reduce the deleterious effect of minor imperfections on the inside pacer neck aperture wall, and to utilize the compression of body fluids that may have leaked past the outer seal to increase the strength of the inner seal rather than weaken it.
Other objects and features of the invention will in part be apparent and in part be pointed out hereinafter.